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  Cryosurgical systemRelated Patent Categories: Surgery, Instruments, Cyrogenic Application, Internal ApplicationThe Patent Description & Claims data below is from USPTO Patent Application 20070244474. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTIONS [0001] The inventions described below relate the field of cryosurgical systems. BACKGROUND OF THE INVENTIONS [0002] Cryosurgery refers to the freezing of body tissue in order to destroy diseased tissue. Minimally invasive cryosurgical systems generally include a long, slender cryoprobe adapted for insertion into the body so that the tip resides in the diseased tissue, and source of cryogenic fluid, and the necessary tubing to conduct the cryogenic fluid into and out of the probe. These cryosurgical systems also include heating systems, so that the probes can be warmed to enhance the destructive effect of the cryoablation and to provide for quick release of the cryoprobes when ablation is complete. [0003] Our own Visica.RTM. cryoablation system has proven effective for the treatment of lesions within the breast of female patients. The system uses Joule-Thompson cryoprobes, and uses argon gas as the cryogenic fluid. The argon gas, supplied at room temperature but very high pressure, expands and cools within the tip of the cryoprobe to generate the cooling power needed to freeze body tissue to cryogenic temperatures. The Visica.RTM. cryoablation system uses high-pressure helium flow through the cryoprobe to heat the probe. The system requires large supplies of argon gas, but is otherwise quite convenient. [0004] Present cryoprobes utilizing Joule-Thomson systems have inherent disadvantages such as inefficient heat transfer and excessive use of cryogen. As a result, these systems require large quantities of gasses under high pressure and high flow rates. Use of high-pressure gasses increases the material costs of surgical systems. This is due to the high cost of materials required for use with systems utilizing high-pressure gases, the high costs associated with obtaining high pressure gases and the large quantities of cryogen required for use with these systems. [0005] Earlier cryoprobes proposed for other surgeries, such as prostrate cryosurgery, used liquid nitrogen, which has the advantage that it is more readily available than argon, and the volume necessary for a given cryosurgical procedure is much smaller then argon. Cryoablation systems using liquid nitrogen, such as the Accuprobe.TM. cryoablation system, have been proposed and used, but these systems have been abandoned in favor of the Joule-Thompson systems. The literature and patent filings indicate that liquid nitrogen systems were plagued by various problems, such as vapor lock and excessive consumption of liquid nitrogen. Proposals to solve these problems, though never successfully implemented, include various schemes to prevent vapor lock and maximize efficiency of the heat exchange. See Rubinsky, et al., Cryosurgical System For Destroying Tumors By Freezing, U.S. Pat. No. 5,334,181 (Aug. 2, 1994) and Rubinsky, et al., Cryosurgical Instrument And System And Method Of Cryosurgery, U.S. Pat. No. 5,674,218 (Oct. 7, 1997), and Littrup, et al., Cryotherapy Probe and System, PCT Pub. WO 2004/064914 (Aug. 5, 2004). Systems like those disclosed in Rubinsky '181, Rubinski '218 and Littrup are complicated and expensive to manufacture. [0006] Rubinsky '181 and '218 are extremely complex systems. The Rubinsky system is directed towards a system that includes a vacuum chamber and means for drawing a vacuum on a reservoir of liquid nitrogen while sub-cooling the liquid nitrogen. Specifically, the system accomplishes the sub-cooling of liquid nitrogen by evaporative cooling induced by using an active vacuum on a reservoir of liquid nitrogen. The liquid nitrogen (LN.sub.2) in Rubinsky flows through a heat exchanger disposed within a vacuum chamber prior to entering the probe through an inlet tube. The LN.sub.2 is sub-cooled to temperatures far below -195.8.degree. C. (sub-cooling) in the vacuum chamber. [0007] Rubinsky takes the drastic approach of sub-cooling the LN2 in an effort to overcome inefficiencies found in traditional cryoprobe systems. Most conventional cryosurgical probe instruments operate with liquid nitrogen or other liquefied gas as the cooling medium. The LN.sub.2 is introduced into the freezing zone of the probe through an inlet tube (which is usually the innermost tube of three concentric tubes). The inlet tube extends into an expansion chamber at the closed probe tip end but terminates a distance from the tip. The LN2 immediately and rapidly vaporizes and undergoes over a one hundred-fold increase in volume. As the liquid vaporizes, it absorbs heat from the probe tip to lower its temperature, theoretically to the normal boiling point of LN2 (about -196.degree. C.). However, in actual practice as liquid nitrogen boils, a thin layer of nitrogen gas inevitably forms on the inner surface of the closed probe tip end. This gas layer has a high thermal resistance and acts to insulate the probe tip freezing zone such that the outside probe tip temperature does not usually fall below about -160.degree. C. This effect is known as the Liedenfrost effect. Other inefficiencies found in traditional cryoprobe systems include vapor lock. Vapor lock occurs when the back pressures produced by the boiling LN.sub.2 reduce the LN.sub.2 flow into the freezing zone, thereby further reducing the efficiency of the probe tip to cool. Rubinsky sub-cools the LN.sub.2 as a way to overcome these inefficiencies [0008] In order to address inefficiencies found in traditional cryoprobe systems, Littrup takes a different approach than Rubinsky. Littrup pressurizes the liquid nitrogen to near critical pressures along the phase diagram to pressures of about 494 psi (nearly 33.5 atmospheres) to overcome the Liedenfrost effect and back pressure. The Littrup system uses a cryotherapy probe with a shaft having a closed distal end adapted to insertion into a body and having a hollow zone within the shaft. A thermally isolated inlet capillary is provided in fluid communication with the hollow zone for providing a flow of liquid towards the hollow zone. An outlet capillary is provided in fluid communication with the hollow zone for providing a flow of liquid away from the hollow zone. A vacuum jacket is adapted to provide thermal insulation of the inlet and outlet capillaries within the shaft. The Littrup device requires two tubes thermally isolated from one another disposed within the shaft of the probe. Working pressures in the Littrup device range from 420 psi to 508 psi (29-35 bars) of pressure. The high pressures required in Littrup necessitate the use of expensive materials and fittings to maintain the cryogen at these pressures and prevent system failure. [0009] To date, the problems inherent in liquid nitrogen systems have led the art to avoid them in favor of gaseous argon systems. What is needed is a cryoprobe system that can utilize liquid nitrogen in a low pressure, low cost and efficient manner. SUMMARY [0010] The devices and methods described below provide for use of liquid nitrogen in cryoablation systems while minimizing the amount of cryogen used during cryosurgical procedures. The system uses cryoprobes of coaxial structure, and is supplied with cryogen from a dewar of liquid nitrogen. The system includes various enhancements to avoid heat transfer from the liquid nitrogen to the system components, and as a result permits use of very low-pressure nitrogen, and, vice-versa, the use of low pressure nitrogen permits use of the various enhancements (which could not be used in a high pressure system). The result is a system that provides sufficient cooling power to effectively ablate lesions, tumors and masses within the breast of female patients while using very little nitrogen and a compact and inexpensive system based on readily available and easy to handle liquid nitrogen. [0011] The system includes a low-pressure liquid nitrogen supply, which preferably uses only 22.5 to 29.4 psi of pressure to provide adequate cooling power for treatment of typical breast lesions. The pressure may be provided by supplying lightly pressurized air into the dewar, by heating a small portion of the nitrogen in the dewar or with a small low pressure pump. For example, our prototype utilizes a compressor commonly used in household aquariums to pressurize the dewar. [0012] The utilization of low pressure liquid nitrogen permits use of polymers for several components, such as the supply hose, the cryoprobe inlet tube, and various hose connectors which are typically made of metal, so that the system is much more efficient and uses very little liquid nitrogen. Additionally, because the liquid nitrogen is lightly pressurized, the boiling point remains low, and the liquid temperature also remains low compared with higher pressure systems. BRIEF DESCRIPTION OF THE DRAWINGS [0013] FIG. 1 illustrates a cryosurgical system which uses liquid nitrogen as a cryogen. [0014] FIG. 2 illustrates a handle potion and supply hose. [0015] FIG. 3 illustrates a supply hose modified to enhance operation of the system of FIG. 1. [0016] FIG. 4 illustrates a sectional view of the dewar. [0017] FIG. 5 illustrates a cryosurgical system with a dewar and a compressor to pressurize the cryogen disposed within the housing of the control system. [0018] FIG. 6 illustrates the control system interface of the cryosurgical system. [0019] FIG. 7 illustrates a cryosurgical system which uses liquid nitrogen as a cryogen and a small heater in the cryogen source to pressurize the cryogen. [0020] FIG. 8 illustrates a cryosurgical system which uses liquid nitrogen as a cryogen and a pump for driving cryogen flow. Continue reading... Full patent description for Cryosurgical system Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Cryosurgical system patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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